Thin film material and method of manufacturing the same

ABSTRACT

A thin film material and a method of manufacturing the thin film material are obtained with which properties of films formed on a substrate can be improved. A superconducting wire  1  includes a substrate  2,  an intermediate thin film layer (intermediate layer  3 ) formed on the substrate and comprised of one layer or at least two layers, and a single-crystal thin film layer (superconducting layer  4 ) formed on the intermediate thin film layer (intermediate layer  3 ). An upper surface (ground surface  10 ) that is the upper surface of at least one layer of the intermediate thin film layer (intermediate layer  3 ) and is opposite to the single-crystal thin film layer (superconducting layer  4 ) is ground.

TECHNICAL FIELD

The present invention relates to a thin film material and a method ofmanufacturing the thin film material. More specifically, the inventionrelates to a thin film material having a single-crystal thin film layerexcellent in crystallinity as well as a method of manufacturing the thinfilm material.

BACKGROUND ART

There are conventional thin film materials that are known, for example,as a superconducting thin film wire having, as an example of asingle-crystal thin film layer, a superconducting layer formed directlyon a substrate (see for example Japanese Patent Laying-Open Nos. 6-31604(Patent Document 1), 6-68727 (Patent Document 2) and 6-68728 (PatentDocument 3)) as well as a superconducting thin film wire having anintermediate thin film layer and a superconducting layer that are formedon a substrate (see for example “Development of High-TemperatureSuperconducting Thin Film Tape Using the ISD Method,” Fujino and sixother authors, SEI Technical Review, September 1999, Vol. 155, pp.131-135 (Non-Patent Document 1)).

Regarding such superconducting thin film wires as mentioned above, it isproposed to grind a surface of the substrate in advance for the purposeof forming such a single-crystal thin film layer as superconductinglayer that has excellent properties (for example high critical currentdensity) (see Patent Documents 1 to 3).

-   -   Patent Document 1: Japanese Patent Laying-Open No. 6-31604    -   Patent Document 2: Japanese Patent Laying-Open No. 6-68727    -   Patent Document 3: Japanese Patent Laying-Open No. 6-68728    -   Non-Patent Document 1: “Development of High-Temperature        Superconducting Thin Film Tape Using the ISD Method,” Fujino and        six other authors, SEI Technical Review, September 1999, Vol.        155, pp. 131-135

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

Regarding the above-described superconducting thin film wire having theintermediate thin film layer and the superconducting layer formed on thesubstrate, in the case where the intermediate thin film layer is formedon a surface of the substrate that has been ground and thereafter thesuperconducting layer is formed on the intermediate thin film layer, itis difficult to sufficiently improve the in-plane orientation of thesuperconducting layer formed as an example of a single-crystal thin filmlayer, since the surface of the intermediate thin film layer has notparticularly undergone such a process as planarization. Consequently,there remains a problem that properties of the single-crystal thin filmlayer thus formed (for example, if the formed single-crystal thin filmlayer is a superconducting layer, such a property as critical currentdensity of the superconducting layer) are not sufficiently improved.

The present invention is made to solve such a problem as describe above.An object of the present invention is to provide a thin film materialand a method of manufacturing the thin film material with whichproperties of a single-crystal thin film layer formed on a substrate canbe improved.

Means for Solving the Problems

A thin film material according to the present invention includes asubstrate, an intermediate thin film layer formed on the substrate andcomprised of one layer or at least two layers, and a single-crystal thinfilm layer formed on the intermediate thin film layer. An upper surfacethat is an upper surface of at least one layer of the intermediate thinfilm layer and that is opposite to the single-crystal thin film layer isground.

Thus, the upper surface of the intermediate thin film layer that isopposite to the overlying thin film layer is ground to be smoothed, andaccordingly such properties as surface smoothness and in-planeorientation of the single-crystal thin film layer formed on the groundupper surface can be improved.

A superconducting thin film material according to the present inventionincludes a substrate, an intermediate thin film layer formed on thesubstrate and comprised of one layer or at least two layers, and asingle-crystal thin film layer formed on the intermediate thin filmlayer. A surface (upper surface) that is a surface of the intermediatethin film layer and that is in contact with the single-crystal thin filmlayer is ground.

Thus, the surface of the intermediate thin film layer that is in contactwith the single-crystal thin film layer is ground to be smoothed, andaccordingly such properties as surface smoothness and in-planeorientation of the single-crystal thin film layer formed on the groundsurface can be improved. In the case where a superconducting thin filmlayer for example is formed as the single-crystal thin film layer, theimproved surface smoothness and in-plane orientation of thesingle-crystal thin film layer (superconducting thin film layer) canprovide improvements in such properties as critical current value andcritical current density of the superconducting thin film layer.

A superconducting thin film material according to the present inventionincludes a substrate, an intermediate thin film layer and asingle-crystal thin film layer formed on the intermediate thin filmlayer. The intermediate thin film layer includes a lower intermediatethin film layer formed on the substrate and comprised of one layer or atleast two layers, and an upper intermediate thin film layer formed onthe lower intermediate thin film layer and comprised of one layer or atleast two layers. A surface (upper surface) that is a surface of thelower intermediate thin film layer and that is in contact with the upperintermediate thin film layer is ground.

Thus, the upper surface of the lower intermediate thin film layer isground to be planarized, and accordingly the planarity of the uppersurface of the upper intermediate thin film layer (upper surfaceopposite to the single-crystal thin film layer) is also improved.Therefore, such properties as surface smoothness and in-planeorientation of the single-crystal thin film layer formed on the upperintermediate thin film layer can be improved. In the case where asuperconducting thin film layer for example is formed as thesingle-crystal thin film layer, the improved surface smoothness andin-plane orientation of the superconducting thin film layer can provideimprovements in such properties as critical current value and criticalcurrent density of the superconducting thin film layer.

A method of manufacturing a thin film material according to the presentinvention includes the steps of preparing a substrate, forming anintermediate thin film layer comprised of one layer or at least twolayers on the substrate, processing by grinding an uppermost surface ofthe intermediate thin film layer, and forming a single-crystal thin filmlayer on the uppermost surface of the intermediate thin film layer thatis ground in the processing step.

Thus, the thin film material of the present invention can easily bemanufactured. Further, since the single-crystal thin film layer can beformed on the uppermost surface of the intermediate thin film layer thathas been ground to exhibit excellent planarity, the surface smoothnessand in-plane orientation of the single-crystal thin film layer can beimproved.

A method of manufacturing a thin film material according to the presentinvention includes the steps of preparing a substrate, forming a lowerintermediate thin film layer comprised of one layer or at least twolayers on the substrate, processing by grinding an uppermost surface ofthe lower intermediate thin film layer, forming an upper intermediatethin film layer comprised of one layer or at least two layers on theuppermost surface of the lower intermediate thin film layer that isground in the processing step, and forming a single-crystal thin filmlayer on the upper intermediate thin film layer.

Thus, the thin film material of the present invention can easily bemanufactured. Further, since the uppermost surface (upper surface) ofthe lower intermediate thin film layer is ground to be planarized, theplanarity of the upper surface of the upper intermediate thin film layer(surface opposite to the single-crystal thin film layer) is alsoimproved. Accordingly, such properties as surface smoothness andin-plane orientation of the single-crystal thin film layer formed on theupper intermediate thin film layer can be improved.

Effects of the Invention

As discussed above, according to the present invention, a thin filmmaterial having a single-crystal thin film layer excellent in surfacesmoothness and in-plane orientation can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic partial cross-sectional view showing a firstembodiment of a superconducting wire according to the present invention.

FIG. 2 is a flowchart illustrating a method of manufacturing thesuperconducting wire shown in FIG. 1.

FIG. 3 is a schematic partial cross-sectional view showing amodification of the first embodiment of the superconducting wire shownin FIG. 1.

FIG. 4 is a flowchart illustrating a method of manufacturing thesuperconducting wire shown in FIG. 3.

FIG. 5 is a schematic partial cross-sectional view showing a secondembodiment of the superconducting wire according to the presentinvention.

FIG. 6 is a flowchart illustrating a method of manufacturing thesuperconducting wire shown in FIG. 5.

FIG. 7 is a schematic partial cross-sectional view showing a thirdembodiment of the superconducting wire according to the presentinvention.

FIG. 8 is a flowchart illustrating a method of manufacturing thesuperconducting wire shown in FIG. 7.

FIG. 9 is a schematic partial cross-sectional view showing amodification of the third embodiment of the superconducting wire of thepresent invention shown in FIG. 7.

FIG. 10 is a schematic partial cross-sectional view showing Example 2 ofthe superconducting wire according to the present invention.

DESCRIPTION OF THE REFERENCE SIGNS

1 superconducting wire, 2 substrate, 3, 3 a-3 f intermediate layer, 4superconducting layer, 10, 20 ground surface, 30, 40 upper surface

BEST MODES FOR CARRYING OUT THE INVENTION

With reference to the drawings, embodiments of the present invention arehereinafter described. In the following drawings, like or correspondingcomponents are denoted by like reference numerals and the descriptionthereof is not repeated.

First Embodiment

Referring to FIGS. 1 and 2 a first embodiment of a superconducting wireof the present invention is described.

As shown in FIG. 1, a superconducting wire 1 is comprised of a substrate2, an intermediate layer 3 and a superconducting layer 4. Substrate 2 isin the shape of a long strip. The upper surface of intermediate layer 3is a surface having undergone a grinding process, namely a groundsurface 10. Thus, superconducting layer 4 is formed on the upper surface(ground surface 10) of intermediate layer 3 that is superior in surfacesmoothness, and accordingly superconducting layer 4 is improved insurface smoothness and in-plane orientation. Consequently,superconducting wire 1 that exhibits excellent superconductingproperties (critical current value and critical current density) can beobtained.

Referring then to FIG. 2, a method of manufacturing superconducting wire1 shown in FIG. 1 is described. According to the method of manufacturingsuperconducting wire 1 shown in FIG. 1, the step of preparing thesubstrate is first carried out as shown in FIG. 2 (S10). Specifically,substrate 2 serving as a base for superconducting wire 1 is prepared. Asthis substrate 2, a strip-shaped metal tape made of such a metal asnickel may be employed.

Next, the step of forming the intermediate layer is carried out (S20).In this step of forming the intermediate layer (S20), intermediate layer3 made of an oxide is formed on the prepared substrate 2. For thisintermediate layer 3, an oxide having such a crystal structure as rocksalt type, fluorite type, perovskite type or pyrochlore type structurefor example may be employed. As a film deposition method to be employedin the step of forming intermediate layer 3 (S20), an arbitrary filmdeposition method may be employed. For example, such a physical vapordeposition method as pulsed laser deposition (PLD) may be employed.

Then, the planarization step is performed (S30). In this planarizationstep (S30), CMP (Chemical Mechanical Polishing) is used to remove theupper surface layer of the aforementioned intermediate layer 3 by apredetermined thickness so as to accomplish the planarization. As amethod to be employed for the planarization, any arbitrary method suchas wet etching or mechanical polishing may be used instead of theaforementioned CMP.

At this time, the surface roughness (Ra) of ground surface 10 (seeFIG. 1) of the planarized intermediate layer 3 is at most 20 nm and morepreferably at most 5 nm.

After this, the step of forming the superconducting layer onintermediate layer 3 with its upper surface planarized is performed(S40). As a film deposition method to be employed in the step of formingsuperconducting layer 4 (S40), any arbitrary film deposition method maybe employed. As employed in forming intermediate layer 3, such aphysical vapor deposition method as pulsed laser deposition may beemployed. Further, in the step of forming superconducting layer 4, theaforementioned PLD or ISD may be employed.

In this way, the superconducting wire shown in FIG. 1 can be obtained.

Referring to FIG. 3, a modification of the first embodiment of thesuperconducting wire of the present invention is described.

A superconducting wire 1 shown in FIG. 3 is basically structuredsimilarly to superconducting wire 1 shown in FIG. 1 except for thestructure of intermediate layer 3. Specifically, in superconducting wire1 shown in FIG. 3, intermediate layer 3 is comprised of two layers thatare a lower intermediate layer 3 a and an upper intermediate layer 3 b.The upper surface of upper intermediate layer 3 b is a ground surface 10having undergone grinding, like the upper surface of intermediate layer3 shown in FIG. 1. This superconducting wire 1 structured in theabove-described manner can also provide similar effects to those of thesuperconducting wire shown in FIG. 1.

Referring to FIGS. 4 and 2 showing flowcharts illustrating the method ofmanufacturing the superconducting wire, a method of manufacturingsuperconducting wire 1 shown in FIG. 3 is described. Here, FIG. 4illustrates a process of forming intermediate layer 3 of superconductingwire 1 shown in FIG. 3.

First, the step of preparing the substrate shown in FIG. 2 is performed(S10). After this, as the step of forming the intermediate layer, thestep of forming the lower intermediate layer shown in FIG. 4 isperformed (S21). In this step of forming lower intermediate layer 3 a(S21), an arbitrary film deposition method may be employed, as themethod used in the step of forming the intermediate layer shown in FIG.2 (S20).

Second, the step of forming the upper intermediate layer is performed(S22). In this step of forming upper intermediate layer 3 b (S22) aswell, an arbitrary film deposition method may be employed.

Then, the planarization step for planarizing the upper surface of upperintermediate layer 3 b (S30) (see FIG. 2) and the step of forming thesuperconducting layer (S40) (see FIG. 2) may be performed. Thus, thesuperconducting wire shown in FIG. 3 can be obtained.

Second Embodiment

Referring to FIG. 5, a second embodiment of the superconducting wire ofthe present invention is described.

As shown in FIG. 5, a superconducting wire 1 is basically structuredsimilarly to superconducting wire 1 shown in FIG. 1, except that theupper surface of a substrate 2 is a ground surface 20 that is ground tobe planarized. In this way as well, similar effects to those of thesuperconducting wire shown in FIG. 1 can be provided. Further, since theupper surface of substrate 2 is also planarized, the in-planeorientation of a superconducting layer 4 that is formed at the uppermostlevel can further be improved. Consequently, the critical current valueas well as the critical current density of superconducting layer 4 canfurther be increased.

Referring to FIG. 6, a method of manufacturing the superconducting wireshown in FIG. 5 is described.

According to the method of manufacturing the superconducting wire shownin FIG. 6, the step of preparing the substrate is first performed (S10),as done for the method of manufacturing the superconducting wire shownin FIG. 2. Then, the planarization step for planarizing the substratesurface is performed (S50). In this planarization step (S50), anarbitrary planarization method may be employed. For example, any of suchmethods as CMP, wet etching and mechanical polishing for example may beemployed.

Here, ground surface 20 of substrate 2 as planarized has a surfaceroughness (Ra) of at most 20 nm, more preferably at most 5 nm.

After this, similarly to the method of manufacturing the superconductingwire shown in FIG. 2, the step of forming the intermediate layer (S20),the planarization step for planarizing by grinding the upper surface ofthe intermediate layer (S30), and the step of forming thesuperconducting layer (S40) are performed. In this way, superconductingwire 1 shown in FIG. 5 can be obtained

Third Embodiment

Referring to FIG. 7, a third embodiment of the superconducting wire ofthe present invention is described.

A superconducting wire 1 shown in FIG. 7 is basically structuredsimilarly to the superconducting wire shown in FIG. 3, except that aground surface 10 is formed at the upper surface of a lower intermediatelayer 3 a in an intermediate layer 3, instead of the upper surface of anupper intermediate layer 3 b in intermediate layer 3, and that the uppersurface of a substrate 2 is ground to form a ground surface 20.Superconducting wire 1 structured in the above-described manner alsoprovides effects similar to those of superconducting wire 1 shown inFIG. 3. Further, since the upper surface of substrate 2 is also theplanarized ground surface 20, the planarity of the upper surface ofintermediate layer 3 can further be improved. Consequently, the in-planeorientation of a superconducting layer 4 can further be improved.Accordingly, such properties as critical current value and criticalcurrent density of superconducting layer 4 can further be improved.

Referring to FIG. 8, a method of manufacturing superconducting wire 1shown in FIG. 7 is described.

As shown in FIG. 8, according to the method of manufacturing thesuperconducting wire, the step of preparing the substrate is firstperformed (S10) similarly to the method of manufacturing thesuperconducting wire shown in FIG. 2. Then, as the method ofmanufacturing the superconducting wire shown in FIG. 6, theplanarization step for the substrate surface is performed (S50). Forthis planarization step (S50), an arbitrary planarization method may beemployed. For example, CMP may be employed to remove the surface layerof substrate 2 by a predetermined thickness.

After this, the step of forming the lower intermediate layer on groundsurface 20 of substrate 2 is performed (S21). Thus, lower intermediatelayer. 3 a (see FIG. 7) is formed.

Subsequently, the planarization step (S30) is performed by using thepolishing for example to partially remove the upper surface of the lowerintermediate layer and thereby accomplish planarization. For thisplanarization step (S30), CMP for example may be employed. In this way,at the upper surface of lower intermediate layer 3 a, ground surface 10(see FIG. 7) is formed.

Following this, the step of forming upper intermediate layer 3 b onground surface 10 of lower intermediate layer 3 a is performed (S22).Here, for the step of forming the lower intermediate layer (S21) and thestep of forming the upper intermediate layer (S22), an arbitrary filmdeposition method may be employed. For example, such a physical vapordeposition as pulsed laser deposition may be employed.

Then, the step of forming superconducting layer 4 on upper intermediatelayer 3 b is performed (S40). In this way, the superconducting wireshown in FIG. 7 can be obtained.

It is noted that, as shown in FIG. 9, each of lower intermediate layer 3a and upper intermediate layer 3 b may be comprised of a plurality oflayers (two layers in FIG. 9). Referring to FIG. 9, a modification ofsuperconducting wire 1 shown in FIG. 7 is described.

As shown in FIG. 9, superconducting wire 1 is basically structuredsimilarly to superconducting wire 1 shown in FIG. 7, except for thestructure of lower intermediate layer 3 a and upper intermediate layer 3b. Specifically, in superconducting wire 1 shown in FIG. 9, lowerintermediate layer 3 a is comprised of a first intermediate layer 3 cformed on ground surface 20 of substrate 2 and a second intermediatelayer 3 d formed on this first intermediate layer 3 c. Further, theupper surface of the second intermediate layer 3 d is a ground surface10. Furthermore, upper intermediate layer 3 b shown in FIG. 9 iscomprised of a third intermediate layer 3 e formed on the secondintermediate layer 3 d and a fourth intermediate layer 3 f formed on thethird intermediate layer 3 e.

Superconducting wire 1 structured in the above-described manner alsoprovides effects similar to those of superconducting wire 1 shown inFIG. 7.

While upper intermediate layer 3 b and lower intermediate layer 3 ashown in FIG. 9 are each comprised of a plurality of layers (two layersin FIG. 9, however, upper intermediate layer 3 and lower intermediatelayer 3 a each may be comprised of an arbitrary number of layers that isat least three), lower intermediate layer 3 a may be comprised of aplurality of layers while upper intermediate layer 3 b may be of asingle layer as shown in FIG. 7. On the contrary, upper intermediatelayer 3 b may be comprised of a plurality of layers and lowerintermediate layer 3 a may be of a single layer as shown in FIG. 7.

The characteristic structures of the superconducting wire, as an exampleof the thin-film material, according to the invention as describedabove, are summarized as follows. Superconducting wire 1 shown in FIGS.1, 3, 5, 7 and 9 as the thin film material includes a substrate 2, anintermediate thin film layer (intermediate layer 3) formed on thesubstrate and comprised of one layer or at least two layers, and asingle-crystal thin film layer (superconducting layer 4) formed on theintermediate thin film layer (intermediate layer 3). An upper surface(ground surface 10 as shown in FIGS. 1, 3 and 5 for example) that is anupper surface of at least one layer of the intermediate thin film layer(intermediate layer 3) and that is opposite to the single-crystal thinfilm layer (superconducting layer 4) is ground. Thus, the upper surfaceof intermediate layer 3 that is opposite to superconducting layer 4 isground to be smoothed, and accordingly such properties as surfacesmoothness and in-plane orientation of superconducting layer 4 formed onthe ground upper surface (ground surface 10) can be improved.

Superconducting wire 1 as the thin film material according to thepresent invention includes, as shown for example in FIGS. 1, 3 and 5, asubstrate 2, an intermediate thin film layer (intermediate layer 3)formed on the substrate and comprised of one layer or at least twolayers, and a single-crystal thin film layer (superconducting layer 4)formed on the intermediate thin film layer (intermediate layer 3). Asurface (ground surface 10) that is a surface of the intermediate thinfilm layer (intermediate layer 3) and that is in contact with thesingle-crystal thin film layer (superconducting layer 4) is ground.

Thus, the upper surface (ground surface 10) of the intermediate thinfilm layer (intermediate layer 3) that is opposite to superconductinglayer 4 is ground to be smoothed, and accordingly such properties assurface smoothness and in-plane orientation of the single-crystal thinfilm layer (superconducting layer 4) formed on the ground upper surface(ground surface 10) can be improved. Accordingly, the improved surfacesmoothness and in-plane orientation of superconducting layer 4 canprovide improvements in such properties as critical current value andcritical current density of superconducting wire 1.

Superconducting wire 1 as the thin film material according to thepresent invention includes, as shown in FIGS. 7 and 9, a substrate 2, anintermediate thin film layer (intermediate layer 3) and a single-crystalthin film layer (superconducting layer 4) formed on intermediate layer3. Intermediate layer 3 includes a lower intermediate thin film layerformed on substrate 2 and comprised of one layer or at least two layers(lower intermediate layer 3 a shown in FIG. 7 or lower intermediatelayer 3 a comprised of first and second intermediate layers 3 c, 3 dshown in FIG. 9) and an upper intermediate thin film layer formed on thelower intermediate thin film layer (lower intermediate layer 3 a) andcomprised of one layer or at least two layers (upper intermediate layer3 b shown in FIG. 7 or lower intermediate layer 3 b comprised of thirdand fourth intermediate layers 3 e, 3 f shown in FIG. 9). An uppersurface (ground surface 10) that is an upper surface of the lowerintermediate thin film layer (lower intermediate layer 3 a) and that isin contact with the upper intermediate thin film layer (upperintermediate layer 3 b) is ground.

Thus, the upper surface of lower intermediate layer 3 a is ground to beplanarized, and accordingly the upper surface (surface opposite tosuperconducting layer 4) of upper intermediate layer 3 b can be improvedin planarity. Therefore, such properties as surface smoothness andin-plane orientation of the single-crystal thin film layer(superconducting layer 4) formed on this upper intermediate layer 3 bcan be improved. The improved surface smoothness and in-planeorientation of superconducting layer 4 can provide improvements in suchproperties as critical current value and critical current density ofsuperconducting layer 4.

Regarding the above-described superconducting wire 1, as shown forexample in FIGS. 5, 7 and 9, the upper surface (ground surface 20) ofsubstrate 2 that is opposite to the intermediate thin film layer(intermediate layer 3) may be ground. In this case, since the uppersurface of substrate 2 is ground in advance, the upper surface (oppositeto superconducting layer 4) of intermediate layer 3 formed on the groundsurface (ground surface 20) or the upper surface of lower intermediatelayer 3 a that is a component of intermediate layer 3 as shown in FIG. 7can be improved in planarity. Thus, in the case where the grinding step(planarization step (S30) shown in FIG. 6) is performed on the uppersurface of intermediate layer 3 that is opposite to superconductinglayer 4 or the grinding step (planarization step (S30) shown in FIG. 8)is performed on the upper surface of lower intermediate layer 3 a,sufficient planarity can be implemented while an amount of grinding iskept small. In this way, the time consumed for the process ofmanufacturing superconducting wire 1 can be shortened and consequentlythe manufacturing cost of superconducting wire 1 can be reduced.

Further, when the upper surface of intermediate layer 3 or the uppersurface of lower intermediate layer 3 a is to be ground, as ground inthe case where the surface of substrate 2 is not ground, the planarityof the upper surface of intermediate layer 3 (or upper surface of lowerintermediate layer 3 a) is ensured to a degree before the upper surfaceof the intermediate or lower intermediate layer is ground. Therefore,the planarity of the upper surface of intermediate layer 3 (or uppersurface of lower intermediate layer 3 a) and the orientation ofintermediate layer 3 can further be improved. Accordingly, suchproperties as the surface smoothness and in-plane orientation of thesingle-crystal thin film layer (superconducting layer 4) formed on theintermediate thin film layer (intermediate layer 3) can further beimproved.

Regarding the above-described thin film material (superconducting wire1), the single-crystal thin film layer (superconducting layer 4) is asuperconducting thin film layer. In this case, as the structure ofsuperconducting wire 1 provided as a thin film material, the structureof the thin film material of the present invention may be used.Therefore, the superconducting thin film layer (superconducting layer 4)may be formed as the single-crystal thin film layer as shown in FIGS. 1and 3 for example, so as to obtain the superconducting thin film layer(superconducting layer 4) that is excellent in surface smoothness andin-plane orientation. Accordingly, the superconducting thin film layer(superconducting layer 4) that is excellent in such properties ascritical current value and critical current density can be obtained.

Regarding the above-described superconducting wire 1, substrate 2 may bemade of a metal. Further, substrate 2 may be in the shape of a longstrip. Intermediate layer 3 may be made of an oxide having a crystalstructure of one of rock salt type, fluorite type, perovskite type andpyrochlore type. For example, intermediate layer 3 may be made of YSZ(yttria-stabilized zirconia), an oxide of a rare earth element likeCeO₂, BZO (BaZrO₃), STO (SrTiO₃) or Al₂O₃ for example. As shown in FIGS.3, 7 and 9, in the case where intermediate layer 3 is comprised of aplurality of layers, intermediate layers 3 a to 3 f constitutingintermediate layer 3 may be made of respective materials different fromeach other. Superconducting layer 4 may be made of an RE-123 typesuperconductor. Thus, since intermediate layer 3 and superconductinglayer 4 are formed on substrate 2 made of a flexible metal,superconducting wire 1 that is easy to deform, bend, for example, andthat serves as a superconducting thin film material having largecritical current value and critical current density can be implemented.

As a method of manufacturing a thin film material according to thepresent invention, a method of manufacturing superconducting wire 1includes the steps of preparing a substrate (S10), forming anintermediate layer 3 as an intermediate thin film layer 3 comprised ofone layer or at least two layers on the substrate (S20, S21, S22),processing by grinding an uppermost surface of intermediate layer 3(planarization step S30 in FIGS. 2 and 6), and forming a single-crystalthin film layer on the uppermost surface (ground surface 10) ofintermediate layer 3 that is ground in the processing step, namely thestep of forming superconducting layer 4 as a superconducting thin filmlayer (the step of forming the superconducting layer in FIGS. 2 and 6)(S40). Thus, superconducting wire 1 as the thin film material of thepresent invention can easily be manufactured. Further, since thesingle-crystal thin film layer (superconducting layer 4) can be formedon the uppermost surface of intermediate layer 3 that is ground toexhibit excellent planarity, the surface smoothness and in-planeorientation of superconducting layer 4 can be improved. Accordingly,such characteristics as critical current value and critical currentdensity of superconducting layer 4 can be improved.

As a method of manufacturing a thin film material according to thepresent invention, a method of manufacturing superconducting wire 1includes the steps of preparing a substrate (S10), forming a lowerintermediate layer 3 a as a lower intermediate thin film layer comprisedof one layer or at least two layers on the substrate (step S21 in FIG.8), processing by grinding the uppermost surface of lower intermediatelayer 3 a (planarization step S30 in FIG. 8), forming an upperintermediate thin film layer (upper intermediate layer 3 b) comprised ofone layer or at least two layers on the uppermost surface of lowerintermediate layer 3 a that is ground in the processing step (step S22in FIG. 8), and forming a single-crystal thin film layer(superconducting layer 4) on upper intermediate layer 3 b, namelyforming a superconducting thin film layer (step S40 of forming thesuperconducting layer in FIG. 8). In this way, superconducting wire 1 ofthe present invention can easily be manufactured. Further, since theuppermost surface (upper surface) of lower intermediate layer 3 a isground to be planarized, the planarity of the upper surface (surfaceopposite to superconducting layer 4) of upper intermediate layer 3 b isalso improved. Thus, such properties as surface smoothness and in-planeorientation of superconducting layer 4 formed on this upper intermediatelayer 3 b can be improved. Accordingly, such properties as criticalcurrent value and critical current density of superconducting layer 4can be improved.

The method of manufacturing superconducting wire 1 discussed abovefurther includes the substrate processing step for grinding a surface ofsubstrate 2 (planarization step S50 for the substrate surface shown inFIGS. 6 and 8). In this case, since the surface of substrate 2 is groundin advance, the planarity of the surface (opposite to superconductinglayer 4) of intermediate layer 3 that is formed on the ground surface(ground surface 20) or the planarity of the upper surface of lowerintermediate layer 3 a as a component of intermediate layer 3 can beimproved. Thus, in the case where the upper surface of intermediatelayer 3 that is opposite to superconducting layer 4 is ground or theupper surface of lower intermediate layer 3 a is ground, sufficientplanarity can be implemented while keeping an amount of grinding small.Further, when the upper surface of intermediate layer 3 or the uppersurface of lower intermediate layer 3 a is to be ground, as ground inthe case where the surface of substrate 2 is not ground, since theplanarity of the upper surface of in intermediate layer 3 (or uppersurface of lower intermediate layer 3 a) is ensured to a degree beforethe upper surface of the intermediate or lower intermediate layer isground, the planarity of the upper surface of intermediate layer 3 (orupper surface of lower intermediate layer 3 a) as well as theorientation of the intermediate thin film layer can further be improved.

EXAMPLE 1

In order to confirm the effects of the present invention, the followingexperiment was conducted. Specifically, a sample of a ComparativeExample as well as samples 1, 2 of Examples were prepared and thecritical current density of the superconducting layer of each sample wasmeasured, as indicated below. Table 1 shows a part of properties and thevalue of the measured critical current density of each sample. TABLE 1Comparative Example Example 1 Example 2 substrate grinding not performednot performed performed intermediate-layer not performed performedperformed grinding surface roughness of 98 98 2.5 substrate (nm) surfaceroughness of 112 8.5 2.1 intermediate layer (nm) full width at half-12.8 10.1 8.1 maximum of the intermediate layers ΔΦ (°) critical current0 0.7 2.1 density of superconducting layer (MA/cm²)

In Comparative Example and Examples 1 and 2, the substrate, theintermediate layer formed on the substrate and the superconducting layerformed on the intermediate layer form the three-layer structure as shownin FIG. 1. As the substrate, a nickel (Ni) alloy substrate was used.This Ni alloy substrate had a surface roughness (Ra) of 98 nm. As theintermediate layer, yttria-stabilized zirconia (YSZ) was deposited bypulsed laser deposition on the Ni alloy substrate. The YSZ had athickness of 1 μm. Further, as the superconducting layer, an oxidesuperconductor of HoBa₂Cu₃O_(y) (y is approximately 6 to 7, morepreferably approximately 7) was used. This material is hereinaftersimply referred to as HoBCO. This superconducting layer was deposited bypulsed laser deposition to a film thickness of 0.25 μm in each ofComparative Example and Examples 1, 2.

The structure of each sample was confirmed. Regarding the sample of theComparative Example, on the Ni alloy substrate as indicated above, YSZwas directly deposited as the intermediate layer to 1 μm without suchprocessing as surface grinding of the substrate. Then, without suchprocessing as grinding of the upper surface of the intermediate layer ofYSZ, the HoBCO superconducting layer was deposited by pulsed laserdeposition to a thickness of 0.25 μm on the intermediate layer.

As for the sample of Example 1, on the Ni alloy substrate, the YSZ asthe intermediate layer was deposited by pulsed laser deposition to 1 μmas done for the sample of the Comparative Example. Then, the uppersurface of this intermediate layer was ground by CMP to remove the uppersurface by a thickness of 0.25 μm. This grinding process may be atwo-step grinding process. Specifically, the first step is CMP using acommon slurry for removing the upper surface of the intermediate layerby a predetermined thickness and the subsequent second step is grindingthe upper surface of the intermediate layer using an abrasive clothtogether with water instead of slurry (mechanical grinding). Accordingto this approach, the common slurry is first used to perform normal CMPso as to carry out the grinding at a certain grinding rate (thethickness removed by grinding per unit time), thereafter the mechanicalgrinding is performed using water instead of slurry, and thus theprecision in controlling the thickness removed by grinding can beimproved, while the grinding rate decreases. Accordingly, both of theshortened processing time required for grinding and the improvement inprecision in controlling the removed thickness can simultaneously beimplemented to a degree. Further, for this grinding, any mechanicalgrinding method may be employed instead of CMP or another arbitrarymethod (wet etching for example) may be employed. On this intermediatelayer having undergone this grinding, the HoBCO superconducting layerwas deposited by pulsed laser deposition to a film thickness of 0.25 μmas done in the Comparative Example.

As for the sample of Example 2, the surface of the Ni alloy substratewas ground by CMP for surface grinding of the substrate. In thisgrinding process for the surface of the Ni alloy substrate, anyarbitrary grinding method that is applicable to the grinding process forthe intermediate layer discussed above may be used. Further, in thegrinding process for the substrate surface, the surface of the substratewas ground by removing the surface by a thickness of 5 μm. As a result,the substrate surface had a surface roughness (Ra) of 2.5 nm. On thesubstrate surface having undergone the grinding process, the YSZ as theintermediate layer was deposited by pulsed laser deposition to athickness of 1 μm. Then, the upper surface of the YSZ as theintermediate layer was ground by CMP by removing the surface by athickness of 0.25 μm. Further, on the YSZ as the intermediate layerhaving undergone the grinding process, the HoBCO superconducting layerwas deposited by pulsed laser deposition to a thickness of 0.25 μm.

As seen from Table 1, the value of the surface roughness of the YSZ asthe intermediate layer is smaller in Examples 1, 2 as compared with thatof the Comparative Example. Further, a comparison of the surfaceroughness of the YSZ as the intermediate layer between Example 1 andExample 2 shows that the value in Example 2 is smaller than that ofExample 1. The reason therefor seems to be that, by grinding thesubstrate surface, the value of the surface roughness of the substrateserving as the underlying layer in Example 2 is allowed to be smallerthan that of Example 1.

It is also seen from Table 1 that the value of the full width athalf-maximum of the YSZ layer serving as the intermediate layer inExamples 1 and 2 is smaller than that in the Comparative Example. Inaddition, the value of the half width of the YSZ layer serving as theintermediate layer is smaller in Example 2 than Example 1. In otherwords, it is seen that the sample in Example 2 is most excellent incrystal orientation of the YSZ layer. Here, the half width (ΔΘ) refersto a characteristic value measured by the X-ray pole figure measurementthat is a characteristic value indicating the crystal orientation of theYSZ layer.

Further, the critical current density of the superconducting layer wasmeasured for each of the Comparative Example and Examples 1 and 2. As aresult, as seen from Table 1, the critical current density of thesuperconducting layer in the Comparative Example is 0 while that is 0.7in Example 1 and is 2.1 in Example 2. In other words, it is seen thatthe critical current density is larger in Example 2 than that in Example1.

EXAMPLE 2

As a preferred example of the thin film material of the presentinvention, a superconducting wire 1 as shown in FIG. 10 was produced.With reference to FIG. 10, a description is given of superconductingwire 1 according to the present invention.

As shown in FIG. 10, superconducting wire 1 of the present invention hasa first intermediate layer 3 c formed on a substrate 2. A secondintermediate layer 3 d is formed on the first intermediate layer 3 c. Alower intermediate layer 3 a is comprised of the first intermediatelayer 3 c and the second intermediate layer 3 d. On the secondintermediate layer 3 d, an upper intermediate layer 3 b is formed. Onupper intermediate layer 3 b, a superconducting layer 4 is formed.

The upper surface of substrate 2 is a ground surface 20 that has beenground. The upper surface of the second intermediate layer 3 d (namelythe upper surface of lower intermediate layer 3 a) is a ground surface10 that has been ground. As a method of grinding, CMP is used asdescribed in connection with Example 1. Instead, another arbitrarygrinding method may be employed.

As substrate 2, the Ni alloy substrate is used as an example of themetal substrate. Further, as a material for the first intermediate layer3 c, ceria (cerium oxide) is used. This first intermediate layer 3 c isa so-called seed layer for providing good orientation to the secondintermediate layer 3 d for example, and another material may also beused for the first intermediate layer. The first intermediate layer 3 cmay have thickness T1 of at most 1 μm for example.

As a material for the second intermediate layer 3 d, YSZ is used. Thesecond intermediate layer 3 d is formed as an anti-diffusion layer forpreventing elements that are constituents of superconducting layer 4formed above from diffusing toward substrate 2. In order to allow thisanti-diffusion capability to surely be exhibited, thickness T2 of thesecond intermediate layer 3 d is set to be relatively larger thanrespective thicknesses of other intermediate layers (thickness T1 of thefirst intermediate layer 3 c and thickness T3 of upper intermediatelayer 3 b). For example, thickness T2 of the second intermediate layer 3d may be at most 4 μm. As a material for the second intermediate layer 3d, any arbitrary material may be used instead of YSZ.

As a material for upper intermediate layer 3 b, ceria (cerium oxide) forexample is used. Upper intermediate layer 3 b is so-calledlattice-matched layer and is provided with the purpose of forming alayer having a lattice constant relatively close to the lattice constantof superconducting layer 4 so as to form superconducting layer 4 withgood orientation on the upper surface of the upper intermediate layer.Thickness T3 of upper intermediate layer 3 b may be at most 1 μm forexample. As a material for upper intermediate layer 3 b, any arbitrarymaterial may be used instead of ceria.

As superconducting layer 4, the HoBCO superconducting layer is used.This HoBCO superconducting layer is deposited by pulsed laser depositionas done for the sample of Example 1. The thickness of the HoBCOsuperconducting layer may be 0.25 μm for example.

The upper surface of substrate 2 is ground surface 20 that has beenground using for example CMP and that may have a surface roughness (Ra)of 2.5 nm for example. Thus, the upper surface of substrate 2 is groundsurface 20 and accordingly the planarity of the upper surface ofsubstrate 2 serving as an underlying layer of intermediate layer 3(second intermediate layer 3 d for example) can be ensured. As a result,the initial surface roughness of the surface to be ground ofintermediate layer 3 can be reduced. Therefore, in the case where the(upper) surface of intermediate layer 3 (second intermediate layer 3 dfor example) is ground to achieve a predetermined surface roughness, anamount of grinding can be reduced and thus the time required for themanufacturing process of the superconducting wire can be shortened.Further, since the upper surface of substrate 2 serving as an underlyinglayer is ground surface 20 with good planarity, the orientation of theintermediate layer (particularly lower intermediate layer 3 a) can beimproved.

Furthermore, the upper surface of the second intermediate layer 3 d isalso ground surface 10 having undergone the grinding process using CMPfor example. The surface roughness (Ra) of the second intermediate layer3 d may be for example 2.1 nm. Thus, the upper surface of the secondintermediate layer 3 d is ground surface 10 so that the layer formed onthe second intermediate layer 3 d (upper intermediate layer 3 b andsuperconducting layer 4) can be improved in orientation.

In addition, the second intermediate layer 3 d serves as ananti-diffusion layer and thus has relatively large thickness T2 asdescribed above. In the case where film thickness T2 is thus large, theplanarity of the upper surface of the second intermediate layer 3 dtends to be worse as film thickness T2 is larger. In other words, underthe condition that respective underlying layers of the firstintermediate layer 3 c, the second intermediate layer 3 d and upperintermediate layer 3 b are the same, the upper surface of the secondintermediate layer 3 d tends to have the largest surface roughness.Therefore, the upper surface of the second intermediate layer 3 d thathas the largest surface roughness (the worst planarity) can be ground toprovide ground surface 10 so as to most effectively obtain intermediatelayer 3 having excellent planarity.

Moreover, the upper surface of the second intermediate layer 3 d (groundsurface 10) could have strain accumulated due to the grinding process.Presence of such a defect as strain could influence orientation forexample of superconducting layer 4 in the case where superconductinglayer 4 is formed directly on this ground surface 10. Therefore, upperintermediate layer 3 b is formed on ground surface 10 andsuperconducting layer 4 is formed on this upper intermediate layer 3 b.Thus, even if such a defect is present in ground surface 10, filmproperties (such a property as orientation) of superconducting layer 4can be prevented from being influenced.

In superconducting wire 1 shown in FIG. 10, only the upper surface ofthe second intermediate layer 3 d may be ground. If thickness T2 of thesecond intermediate layer 3 d is sufficiently small for example, onlythe upper surface of substrate 2 may be ground to form ground surface20.

In addition, upper surface 30 of the first intermediate layer 3 c orupper surface 40 of upper intermediate layer 3 b for example may beground to provide a ground surface. For example, upper surface 30 of thefirst intermediate layer 3 c may be a ground surface to further improvethe orientation of the second intermediate layer 3 d and upperintermediate layer 3 b. Further, the planarity of the upper surface inthe initial state of the second intermediate layer 3 d for exampleformed on the first intermediate layer 3 c can be improved, so that theamount of grinding can be reduced in the grinding process for grindingthe upper surface of the second intermediate layer 3 d with the purposeof providing a predetermined surface roughness. Moreover, when uppersurface 40 of upper intermediate layer 3 b is provided as a groundsurface, the orientation of superconducting layer 4 can further beimproved.

It should be considered that embodiments and examples disclosed here arepresented in all respects by way of illustration and example, not by wayof limitation. It is intended that the scope of the present invention isdefined not by the embodiments but by claims and involves allmodifications in the meaning and range equivalent to the claims.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a thin film material having asingle-crystal thin film layer. In particular, the invention isapplicable to a thin film material having such a single-crystal thinfilm layer as superconducting layer required to be excellent in suchproperties as surface smoothness and in-plane orientation.

1. A thin film material comprising: a substrate; an intermediate thinfilm layer formed on said substrate and comprised of one layer or atleast two layers; and a single-crystal thin film layer formed on saidintermediate thin film layer, wherein an upper surface that is an uppersurface of at least one layer of said intermediate thin film layer andthat is opposite to said single-crystal thin film layer is ground.
 2. Athin film material comprising: a substrate; an intermediate thin filmlayer formed on said substrate and comprised of one layer or at leasttwo layers; and a single-crystal thin film layer formed on saidintermediate thin film layer, wherein a surface that is a surface ofsaid intermediate thin film layer and that is in contact with saidsingle-crystal thin film layer is ground.
 3. A thin film materialcomprising: a substrate; an intermediate thin film layer including alower intermediate thin film layer formed on said substrate andcomprised of one layer or at least two layers and an upper intermediatethin film layer formed on said lower intermediate thin film layer andcomprised of one layer or at least two layers; and a single-crystal thinfilm layer formed on said intermediate thin film layer, wherein asurface that is a surface of said lower intermediate thin film layer andthat is in contact with said upper intermediate thin film layer isground.
 4. The thin film material according to claim 1, wherein an uppersurface of said substrate that is an upper surface opposite to saidintermediate thin film layer is ground.
 5. The thin film materialaccording to claim 1, wherein said single-crystal thin film layer is asuperconducting thin film layer.
 6. The thin film material according toclaim 5, wherein said substrate is made of a metal, said intermediatethin film layer is made of an oxide having a crystal structure of one ofrock salt type, fluorite type, perovskite type and pyrochlore type, andsaid superconducting thin film layer is made of an RE-123 typesuperconductor.
 7. A method of manufacturing a thin film material,comprising the steps of: preparing a substrate; forming an intermediatethin film layer comprised of one layer or at least two layers on saidsubstrate; processing by grinding an uppermost surface of saidintermediate thin film layer; and forming a single-crystal thin filmlayer on the uppermost surface of said intermediate thin film layer thatis ground in said processing step.
 8. A method of manufacturing a thinfilm material, comprising steps of: preparing a substrate; forming alower intermediate thin film layer comprised of one layer or at leasttwo layers on said substrate; processing by grinding an uppermostsurface of said lower intermediate thin film layer; forming an upperintermediate thin film layer comprised of one layer or at least twolayers on the uppermost surface of said lower intermediate thin filmlayer that is ground in said processing step; and forming asingle-crystal thin film layer on said upper intermediate thin filmlayer.
 9. The method of manufacturing a thin film material according toclaim 7, further comprising the substrate processing step for grinding asurface of said substrate.
 10. The method of manufacturing a thin filmmaterial according to claim 7, wherein said step of forming saidsingle-crystal thin film layer is the step of forming a superconductingthin film layer.
 11. The thin film material according to claim 2,wherein an upper surface of said substrate that is an upper surfaceopposite to said intermediate thin film layer is ground.
 12. The thinfilm material according to claim 3, wherein an upper surface of saidsubstrate that is an upper surface opposite to said intermediate thinfilm layer is ground.
 13. The thin film material according to claim 2,wherein said single-crystal thin film layer is a superconducting thinfilm layer.
 14. The thin film material according to claim 3, whereinsaid single-crystal thin film layer is a superconducting thin filmlayer.
 15. The thin film material according to claim 13, wherein saidsubstrate is made of a metal, said intermediate thin film layer is madeof an oxide having a crystal structure of one of rock salt type,fluorite type, perovskite type and pyrochlore type, and saidsuperconducting thin film layer is made of an RE-123 typesuperconductor.
 16. The thin film material according to claim 14,wherein said substrate is made of a metal, said intermediate thin filmlayer is made of an oxide having a crystal structure of one of rock salttype, fluorite type, perovskite type and pyrochlore type, and saidsuperconducting thin film layer is made of an RE-123 typesuperconductor.
 17. The method of manufacturing a thin film materialaccording to claim 8, further comprising the substrate processing stepfor grinding a surface of said substrate.
 18. The method ofmanufacturing a thin film material according to claim 8, wherein saidstep of forming said single-crystal thin film layer is the step offorming a superconducting thin film layer.